Spindle motor

ABSTRACT

A downsized spindle motor of excellent abrasion and shock resistance is provided. Shaft  8  is fit into sleeve  5.  Flange  11  is fixed to an end of shaft  8.  A radial bearing is formed on the faces of shaft  8  and sleeve  5,  the faces are opposite closely to each other. Face  17  of flange closely faces face  16  of thrust plate  12,  thereby forming a thrust bearing. The other face  22  of thrust plate  12  is caulked with tip  21  of sleeve  5  and fixed to each other by adhesive  27.  Tapering section  6  is provided to an upper end of sleeve  5.

FIELD OF THE INVENTION

[0001] The present invention relates to a spindle motor to be mountedto, for instance, a hard disc drive, an optical disk drive, amagneto-optical disc drive, a magnetic disc drive and a polygon mirror.

BACKGROUND OF THE INVENTION

[0002] Various kinds of spindle motors are available in the market, andthus a key component of the spindle motor, i.e., a fluid bearing devicehas numbers of types. Many of the fluid bearing devices include acylindrical sleeve, which bears a load of a shaft in a radial direction.The sleeve surrounds the shaft via an annular space between an outerwall of the shaft and an inner wall of the sleeve. This space is called“a radial bearing space” and filled with lubricant. When a rotor-hubfixedly mounted to a first end of the shaft rotates,hydrodynamic-pressure generating grooves (e.g. herringbones grooves)generate dynamic pressure in the lubricant, so that a radial bearing isformed. The grooves are provided on the outer wall of the shaft and theinner wall of the sleeve.

[0003] A disc-shaped thrust plate is fixed to a second end of the shaft,and herringbone grooves, for instance, are provided to at least one ofan upper face or a lower face of the thrust plate. Lubricant is filledinto the grooves, so that a thrust bearing is formed in order to bear aload in an axial direction.

[0004] The spindle motor and bearing devices discussed above aredisclosed in Japanese Patent Application Non-examined Publication No.2000-113582 (hereinafter called “prior art 1”). Prior art 1 teaches thefollowing points in order to prevent the lubricant from splashing outfrom the bearings: (a) A slope flaring downward in the axial directionis provided on an outer wall of a supporting member, namely, the sleeve.(b) A slope is provided to an upper end of the supporting member so thata space of a thrust bearing flares outward in the radial direction. Thisspace is called a thrust bearing space. (c) Oil repellent made offluorine-based material is applied to a tapering-sealed section in orderto prevent oil-migration, i.e., lubricant such as oil, leaks out fromthe bearings.

[0005] Japanese Patent Application Non-examined Publication No.2000-121986 (prior art 2) discloses an idea that lubricant in a radialbearing space is steadily retained, which prevents the lubricant fromsplashing out or leaking out of the space. In other words, an annularrecess is provided on an inner wall of a sleeve, and the recess has aslope flaring toward an opening of the sleeve. FIG. 6 of prior art 2illustrates that a conical section 103 c is provided at an opening endof sleeve 103, and conical section 103 c has a slope recessed from theouter wall to the inner wall. When shaft 102 is inserted into sleeve 103in assembling the motor, even if the lubricant overflows from a bearingspace, the overflowed lubricant flows back to the space along thisconical section 103 c provided at the end face of sleeve 103. Thisstructure prevents the lubricant from splashing out from the bearingspace.

[0006] Both of prior art 1 and prior art 2 disclose the idea ofpreventing the lubricant from leaking out. Prior art 1 discloses thatthe slope is provided to an outer wall of the sleeve, and the slopeflares downward in the axial direction in order to prevent the lubricantfrom splashing out. Indeed this structure prevents the lubricant,retained in the thrust bearing space, from splashing out; however, priorart 1 does not disclose anything about the problems and their solutionsin filling the lubricant into the thrust bearing space.

[0007] Prior art 2 raises the problem that the lubricant overflows whena shaft is inserted into a sleeve in assembling the spindle motor, andproposes the solution that a slope is provided to an end face of thesleeve. However, according to prior art 2, surplus lubricant ispreferably prepared before the assembly because prior art 2 refers to amethod of inserting the shaft into the sleeves in which the lubricant isfilled.

SUMMARY OF THE INVENTION

[0008] The present invention aims to provide a spindle motor comprisesthe following elements:

[0009] (a) a shaft;

[0010] (b) a flange fixedly mounted to a first end of the shaft andhaving a diameter greater than that of the shaft;

[0011] (c) a cylindrical sleeve to be fit to the shaft;

[0012] (d) a radial bearing space formed between an outer wall of theshaft and an inner wall of the sleeve opposite closely to the outer wallof the shaft;

[0013] (e) a rotor hub fixed to a second end of the shaft and facing anupper end of the sleeve;

[0014] (f) a thrust plate disposed closely and opposite to the flange;

[0015] (g) a thrust bearing space formed between the faces, oppositeclosely to each other, of the flange and the thrust plate;

[0016] (h) lubricant retained in the thrust bearing space; and

[0017] (i) a tapering section provided to an upper end of the sleeve.

[0018] This structure allows a thrust bearing to bear an axial load ofthe shaft, because the flange has the diameter greater than that of theshaft, and the thrust bearing is disposed between the flange and thethrust plate, both of which faces closely each other. Further, atapering section is provided to the upper end of the sleeve, and thisstructure can store an enough amount of the lubricant to be filled intothe radial bearing space. The construction discussed above restraintsthe lubricant from splashing or leaking out from the sleeve, and lowersa pressure applied to the lubricant so that bubbles do not occur in thelubricant. As a result, a spindle motor having a longer service life isobtainable.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a sectional view of an essential part of a spindle motorin accordance with a first exemplary embodiment of the presentinvention.

[0020]FIG. 2 is an enlarged view of a part of the spindle motor shown inFIG. 1.

[0021]FIG. 3 shows steps of manufacturing a spindle motor in accordancewith a third exemplary embodiment of the present invention.

[0022]FIG. 4 illustrates an intermediate style of a spindle motor inaccordance with a fourth exemplary embodiment of the present invention.

[0023]FIG. 5(a) and FIG. 5(b) illustrate a tapering section of a spindlemotor in accordance with a fifth exemplary embodiment of the presentinvention.

[0024]FIG. 6 illustrates a tapering section of the spindle motor inaccordance with the fifth exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS First ExemplaryEmbodiment

[0025]FIG. 1 is a sectional view of an essential part of a spindle motorin accordance with the first exemplary embodiment of the presentinvention. Spindle motor 1 includes inner cylinder 3 and outer cylinder4 respectively on an inner wall and an outer wall of base member 2,which is made of, e.g., die-cast aluminum. Sleeve 5 is provided to aninner wall of inner cylinder 3. Sleeve 5 shapes in substantially acylinder, and is made of brass plated with nickel. Tapering section 5 isprovided to an upper end of sleeve 5, where the upper end surrounds anopening of sleeve 5 and faces a lower face of shoulder 51 of rotor hub50 which is mounted to shaft 8. Adhesive is applied to an outer wall ofsleeve 5, which is then inserted into inner cylinder 3 of base member 2.Sleeve 5 is thus fixed to inner cylinder 3. At the upper end(surrounding the opening), tapering section 6 is provided. On inner wall9 of sleeve 5, for instance, two lubricant reservoirs 26 are prepared.

[0026] Tapering section 6 has an upgrade from an inner side to an outerside of sleeve 5, i.e., from the side of shaft 8 to the side of innercylinder 3. This structure maximizes distance L1 between shoulder 51 andan inner section of sleeve 5, and minimizes distance L2 between shoulder51 and outer section of sleeve 5. This structure produces air-flow atthe upper end of sleeve 5 against a force which splashes or leaks thelubricant along the upgrade of tapering section 6, so that the lubricantis prevented from splashing or leaking out.

[0027] In this first embodiment, a shape of the upper end of sleeve 5 isvaried, and the distances between rotor hub 50 and sleeve 5 are preparedaccording to the variation; however, parts of rotor hub 50 can bechanged in shape, instead. Alternatively, both of sleeve 5 and hub 50can be changed in shape, so that the air-flow can be produced. Theair-flow will be detailed in the fifth exemplary embodiment.

[0028] At least one of outer wall of shaft 8 or inner wall of sleeve 9has, e.g., herringbone grooves 10. In this first embodiment, herringbonegrooves 10 are provided to the outer wall of shaft 8. The face of shaft8, on which herringbone grooves 10 are formed, and a corresponding innerface of sleeve 5 form radial bearing space 24, which is a part of aradial bearing. Herringbone grooves 10 are filled with lubricant such asoil. Grooves 10 with the lubricant works as a fluid bearing andgenerates dynamic pressure in the radial direction when shaft 8 spins.

[0029] Disc-shaped metal unit 11 (flange) is welded by laser to a firstaxial end of shaft 8. Flange 11 is, for instance, a hollow disc and madeof stainless steel SUS4202J2. Flange 11 has a diameter greater than thatof shaft 8, and a ring-shaped metal unit, of which center part ishollowed out, is also included as flange 11. In the first embodiment,ring-shaped flange 11 is employed. Face 17 of flange 11 closely facesface 16 of thrust plate 12. At least one of face 16 or face 17 has,e.g., herringbone grooves, thereby forming a thrust bearing, which bearsan axial load of shaft 8.

[0030] In this specification, when it is not needed to distinguish theradial bearing space from the thrust bearing space, a general expressionof “bearing space” is used.

[0031] Shaft 8 comprises two sections, a first section has a smallerdiameter and a second section has a larger diameter. The first sectioncan be formed by providing a protrusion or a recess on an end of shaft8. In other words, shaft 8 is not a uniform cylinder, but an end ofshaft 8 has a non-flat face. Flange 11 also has a non-flat face whichfits into the non-flat face of shaft 8. Therefore, flange 11 preferablyhas a recess, protrusion or hollow section 13, so that flange 11 can befit to the end of shaft 8 with ease. In FIG. 1, shaft 8 has protrusion28 as the first section having a smaller diameter, and flange 11 hashollow section 13 as a non-flat face.

[0032]FIG. 1 is a sectional view of an essential part of a spindle motorin accordance with the first exemplary embodiment of the presentinvention. In FIG. 1, a left side of shaft 8 is omitted, because thespindle motor is substantially symmetric with respect to shaft 8.

[0033] One of the advantages of the spindle motor of the presentinvention is that shaft 8 has protrusion 28, which provides shaft 8 witha larger diameter and a smaller diameter. Protrusion 28 having thesmaller diameter is inserted into hollow section 13 of flange 11, and acontact section between flange 11 and protrusion 28 is welded by laser,so that laser-welded section 14 is formed. This insertion formsreservoir 29 between protrusion 28 and another face 23 of flange 11. Apart of reservoir 29 is closed by the laser welding discussed above,which tightly closes reservoir 29.

[0034] A fine clearance is formed between shoulder 30 of sleeve 5 andanother face 23 of flange 11. This fine clearance leads the lubricantinto thrust bearing space 40, which is formed between face 17 of flange11 and a corresponding part of face 16 of thrust plate 12.

[0035] If end face 15 of protrusion 28 is carefully inserted into hollowsection 13 so as not to hit face 16 of thrust plate 12, hollow section13 is not completely closed, but remains as a hollow section.

[0036] When shaft 8 is inserted into hollow section 13 prepared at anapprox. center of flange 11, a recess is formed in hollow section 13.This recess can be used to define laser-welded section 14. Hollowsection 13 provides a margin for applying the welding as well as avacant space for reserving the lubricant. The spindle motor can be thusdownsized.

[0037] Thrust plate 12 and flange 11 work together to form the thrustbearing which bears the axial load of shaft 8. These two elements can beused as a sealing member of a so called “one-side sealed spindle motor”as shown in FIG. 1. This utilization of the two elements can simplifythe motor structure.

[0038] Peripheral section 18 is provided to outer circumference ofdisc-shaped thrust plate 12. At peripheral section 18, flange 11 doesnot closely opposite to thrust plate 12. This structure is also one ofthe advantages of the present invention. A diameter of thrust plate 12is set greater than that of flange 11, so that peripheral section 18 canbe formed. Peripheral section 18 is useful for arm section 19 of sleeve5 to closely face side wall 20 of flange 11 as well as face 16 of thrustplate 12. This structure allows sleeve 5 to surround firmly flange 11,and allows sleeve 5 to firmly hold thrust 12. Tip section 21 extendingfrom arm section 19 is provided to sleeve 5, and is bent toward anotherface 22, i.e., a rear face, of thrust plate 12 and then caulked. Thecaulked section is fixed by applying adhesive, thereby increasingmechanical strength such as shock resistance.

[0039] On the other axial end of shaft 8, i.e., the end having a largerdiameter, rotor hub 50 is fixed. Hub 50 comprises disc-shaped shoulder51 and arm 52 depending from an outer rim of shoulder 51. Oil fence 60is provided to a part of shoulder 51. Oil fence 60 prevents thelubricant from splashing out from sleeve 5. Dint 53 of approx. 0.1 mmdepth is provided around the place where shaft 8 is mounted. Laserwelding is applied to a contact spot between shaft 8 and dint 53,thereby forming laser welded section 54.

[0040] Cup-shaped section 59 is provided to arm 52, and cup-shapedsection 59 can fixedly hold a disc or the like (not shown). On an innerwall of arm 52, cylindrical magnet 57, which is magnetized N pole and Spole alternately, is fixed.

[0041] Stator core 56 wound with coil 55 is mounted, close to magnet 57,on a part of base member 2. Attracting plate 58 is disposed on anotherpart of base member 2, so that plate 58 faces magnet 57. Attractingplate 58 is made of material having little iron loss, e.g., iron-nickelalloy. Magnet 57 and attracting plate 58 attract magnetically eachother, therefore, even if the spindle motor is used at any angle, theelements thereof are always retained in normal places. In other words,sleeve 5, thrust plate 12, stator core 56, shaft 8, rotor hub 50 and thelike can be firmly retained at predetermined locations.

[0042] When coil 55 is powered, magnetic field is produced at a salientpole of stator core 56, and torque is generated between stator core 56and magnet 57 facing stator 56, thereby rotating rotor hub 50. A harddisc (not shown) clamped by rotor hub 50 thus spins. The rotation of hub50 entails shaft 8 fixed to hub 50 as well as flange 11 fixed to shaft 8to spin. This mechanism allows the lubricant and the herringbone groovesto produce dynamic pressure, so that the spindle motor works.

Second Exemplary Embodiment

[0043]FIG. 2 is an enlarged view of a part of the spindle motor shown inFIG. 1, and particularly details a fitting status between shaft 8 andsleeve 5, and enlarges an end of shaft 8. Herringbone grooves 10 shownin FIG. 1 are omitted in order to simplify FIG. 2. The elements similarto those in FIG. 2 have the same reference marks.

[0044] Shaft 8 including protrusion 28 has two sections, the firstsection has a larger diameter and the second section, i.e., protrusion28, has a smaller diameter. Thickness “t” of flange 11 is at least equalto height “h” of protrusion 28, i.e., h≦t. This relation can form hollowsection 13 between protrusion 28 and thrust plate 12, and form reservoir29 between protrusion 28 and flange 11. The importance of this relationcan be clarified by assuming a relation of h>t, which is in inverserelation to h≦t. If the relation of h>t were established, tip 15 ofprotrusion 28 would hit face 16 of thrust plate 12. When shaft 8 iscarefully inserted into hollow section 13 of flange 11 so as not to hitface 16, reservoir 29 becomes unnecessarily large and tends to trapbubbles. Reservoir 29, which is the space formed between protrusion 28and face 23 of flange 11, does not work well as a lubricant reservoir.Shock resistance also lowers because the space becomes larger.

[0045] In the second embodiment, the dimensions of the critical elementsare prepared as follows:

[0046] height of protrusion 28: h=0.35 mm,

[0047] thickness of flange 11: t=0.50 mm, and

[0048] a fitted depth of protrusion 28 into hollow section 13: h1=0.25mm.

[0049] According to these dimensions, the height of reservoir 29:h2=h−(t−h1), and the height of hollow section 13: h3=(t−h1). In thisembodiment, the height of reservoir 29: h2=0.10 mm, or 100 μm, and theheight of hollow section 13: h3=0.25 mm, or 250 μm.

[0050] In the spindle motor of the present invention, the height “h” ofprotrusion 28, the thickness “t” of flange 11, and the fitted depth “h1”of the second section of protrusion 28 to flange 11 are predetermined,then the height “h2” of reservoir 29 and the height “h3” of hollowsection 13 can be determined at given sizes.

[0051] Reservoir 29 can be formed by arranging shaft 8, sleeve 5 andflange 11, namely, these three elements are respectively shaped inpredetermined forms and located such that the three elements faceclosely each other, so that three spaces are created. One of the spacesis closed by applying laser welding, so that reservoir 29 is created. Inother words, the lubricant supplied via radial bearing space 24, whichis formed between shaft 8 and sleeve 5, runs into face 23 of flange 11and branches into space 25 and reservoir 29. One of the branches isstopped by laser welding section 14, and retained there. Reservoir 29shut up with laser welding section 14 is tightly closed, thus thelubricant hardly leaks out, and mechanical strength of reservoir 29increases.

[0052] Space 25 leads the lubricant into thrust bearing space 40 formedbetween face 17 of flange 11 and face 16 of thrust 12, and it alsospecifies an axial movable range of shaft 8 as well as of rotor hub 50.The size of space 25 can be arbitrarily determined based on the heightand shape of shoulder 30 of sleeve 5. It is preferably set at not lessthan 0.005 mm and not more than 0.05 mm.

[0053] The presence of reservoir 29 is useful for adjusting an overallheight of the spindle motor, and effective for absorbing dimensionaldispersion of shaft 8.

Third Exemplary Embodiment

[0054]FIG. 3 shows steps of manufacturing a spindle motor in accordancewith the third exemplary embodiment of the present invention. Accordingto method 100 of assembling spindle motor 1 of the present invention,flange 11 is fixed to a first end of shaft 8 by laser welding, as shownin step 102, so that flange 11 is integrated into shaft 8. Flange 11 hasa diameter larger than that of shaft 8.

[0055] Step 104 shows that shaft 8 is fit into sleeve 5. A second end ofshaft 8 is inserted into sleeve 5, the second end being the other endthan the first end where flange 11 is fixed, so that shaft 8 is fit tosleeve 5. As a result, an outer wall of shaft 8 faces inner wall 9 ofsleeve 5 via an annular fine space. This fine space has a width ofseveral μm and forms radial bearing space 24 which bears a radial loadof shaft 8.

[0056] Step 106 shows that thrust plate 12 faces closely flange 11. Face16 of thrust plate 12 is closely placed opposite to face 17 of flange11. These two faces, facing each other, form a thrust bearing whichbears an axial load of shaft 8. Because thrust plate 12 has a largerdiameter than that of flange 11, peripheral section 18 is formed onplate 12, and peripheral section 18 does not face flange 11.

[0057] Step 108 shows that thrust plate 12 is fixed to sleeve 5, therebysealing a lower end of sleeve 5. Arm 19 of sleeve 5 is placed onperiphery section 18 which does not face flange 11, so that an outer rimof disc-shaped flange 11 is surrounded by cylindrical sleeve 5. Thelocations of sleeve 5, flange 11 and shaft 8 are thus steadily fixed.Tip section 21 extending from arm 19 is caulked with rear face 22 ofthrust plate 12, and adhesive 27 is applied on rear face 22 for sealing.

[0058] Step 110 shows that a visual inspection and a sealing inspectionare carried out. In the visual inspection, shapes and displacements ofthrust plate 12 and sleeve 5 are inspected. Thrust plate 12 is utilizedas a sealing member of the spindle motor. In the sealing inspection,air-tightness of these elements is tested, thus an air-leak tester ispreferably used.

[0059] Step 112 shows that lubricant is applied to a place where shaft 8faces an upper end of sleeve 5. Simple composition oil disclosed inJapanese Patent Application Non-Examined Publication No. 2000-179552 canbe used as the lubricant. Substance including magnetic fluid disclosedin Japanese Patent Application Non-Examined Publication No. H08-259982can be also used as the lubricant.

[0060] Step 114 shows that fluid bearing device 70, later shown in FIG.4, is left in vacuum atmosphere. In other words, shaft 8, sleeve 5,flange 11, thrust plate 12 and adhesive 27, which fixes tip section 21of sleeve 5 to thrust plate 12, are exposed in the vacuum. Fluid bearingdevice 70 is a semi-finished product of the spindle motor, and yet, itis a key component of the motor. Fluid bearing device 70 is left in,e.g., a vacuum chamber having a degree of vacuum not more than 100 Torr.

[0061] Step 116 shows that fluid bearing device 70 left in the vacuum isrestored to a normal condition. At this moment, pressure differenceoccurs between the atmospheric pressure and the vacuum in bearingspaces, so that the lubricant is filled into the bearing spaces.

[0062] Step 118 finally shows that rotor hub 50 is welded to an end ofshaft 8 by laser. Hub 50 includes shoulder 51 and arm 52, andsubstantially shapes in a disc. A hole (not shown) is punched at acenter of hub 50, and shaft 8 is fit into this hole.

[0063] Dint 53 is provided near to the center, where shaft 8 is fit, ofshoulder 51. Dint 53 and shaft 8 are welded by laser at a spot whereboth the elements contact with each other, and laser welded section 54is formed. The presence of dint 53 eliminates a margin for welding,therefore, the spindle motor can be downsized. Dint 53 is also used as adefining section for specifying the place to be welded, so that laserwelded section 54 can be provided exactly at a predetermined place.

[0064]FIG. 3 shows essential steps for completing the spindle motor;however, those steps do not cover all the steps. For instance, a step offitting sleeve 5 to base member 2, and a step of fixing stator core 56and attracting plate 58 to base member 2 are needed for completing thespindle motor, but these steps are omitted from FIG. 3. A part of theassembly procedure can be changed, and another step can be added basedon a designing request.

Fourth Exemplary Embodiment

[0065]FIG. 4 illustrates a fluid bearing device, a key component of aspindle motor, in accordance with the fourth exemplary embodiment of thepresent invention. When step 112 shown in FIG. 3 is finished, fluidbearing device 70 is completed. Fluid bearing device 70 is distinguishedfrom spindle motor 1, because sleeve 5 is not yet fit into base member2, or rotor hub 50 is not yet fixed to an end of shaft 8 in device 70.

[0066] In fluid bearing device 70, a first face of flange 11 is fixed toa first end of shaft 8, and a second face of flange 11 closely faces afirst face of thrust plate 12. A second face of thrust plate 12 iscaulked with tip section 21 of sleeve 5. Adhesive 21 is applied to aplace where second face 22 of thrust plate 12 closely faces tip section21, so that this place is fixed and sealed. Further, lubricant isapplied to tapering section 6 and its vicinity, where sleeve 5 closelyfaces shaft 8. Fluid bearing device 70 discussed above is anintermediate style of the spindle motor before the spindle motor iscompleted. Indeed device 70 is the intermediate style; however, thisfluid bearing device 70 can be treated as one component. This is one ofadvantages of the present invention.

[0067] A function test of fluid bearing device 70 includes, forinstance, visual inspections on sleeve 5 and thrust plate 12 about shapeand displacement, and an air-leak test on air-tightness. Since thespindle motor is separated into some units, e.g., a fluid bearingdevice, these tests can be done with ease. Because no lubricant ishandled at the test stage, the air-leak tester and other apparatuses arekept free from contamination.

[0068] Oil repellent applied to tapering section 6 lowers surfacetension of the lubricant, so that it is useful to restraint thelubricant from splashing out from sleeve 5. The oil repellent makes iteasier to wipe out the lubricant leaking out to the upper end of sleeve5.

[0069] Fluid bearing device 70 does not necessarily require taperingsection 6 to be provided to sleeve 5. Because, an advantage of thefourth embodiment does not exist in a method of fitting shaft 8 intosleeve 5 whose inner wall 9 is pre-applied with the lubricant, butexists in a method of fitting shaft 8 into sleeve 5 before the lubricantis applied to inner wall 9 of sleeve 5. Therefore, according to thismethod, an amount of lubricant supposed to overflow when shaft 8 isinserted into sleeve 5 can be saved. In FIG. 3, shaft-tapering 31 isprovided to a part of shaft 8. This will be detailed in the fifthembodiment.

Fifth Exemplary Embodiment

[0070]FIG. 5 and FIG. 6 illustrate appropriate shapes of shaft 8 and anupper end of sleeve 5 for realizing an objective of the presentinvention. FIG. 5(a) illustrates a status where the upper end of sleeve5 is applied with lubricant 7, and FIG. 5(b) shows an enlarged view oftapering section 6 and a part of shaft 8 near to tapering section 6.FIG. 6 illustrates how tapering section 6A works.

[0071] As shown in FIG. 5(a), shaft-tapering 31, including a conicalface followed by a cylindrical face, is provided to shaft 8. Centersection 32 of shaft-tapering 31 substantially corresponds to end section33 of tapering section 6 provided to the upper end of sleeve 5. Thisstructure can provides a rather large space near to end section 33 oftapering section 6.

[0072] End section 33 of tapering section 6 works as an outlet forsupplying or filling the lubricant smooth into radial bearing space 24and thrust bearing space 40. Thus a given space is preferably reservedaround end section 33 for working well as the outlet. Shaft-tapering 31provided to shaft 8 enlarge some space for the outlet and furthersmoothens the supply or filling of the lubricant.

[0073] Shaft-tapering 31 together with tapering section 6 of sleeve 5forms wider-path 34, thus a space where lubricant 7 is retainedincreases. Therefore, a pressure applied to the lubricant is reduced,which restrains bubbles from occurring. A space around end section 33 oftapering section 6, i.e., the outlet, is preferably not enlarged,because the enlargement would incur splash-out of the lubricant fromsleeve 5. However, end section 33 protrudes toward center section 32 ofshaft-tapering 31, and this structure does not invite suchinconvenience.

[0074] End section 33 of tapering section 6 faces reservoir 26 formed oninner wall 9 of sleeve 5 via radial bearing space 24. This structureallows a user to supply or fill the lubricant smooth from taperingsection 6 into reservoir 26, which assists the lubricant in flowing fromtapering section 6 smooth into radial bearing space 24 and thrustbearing space 40. This structure reduces the pressure applied to thelubricant, and restrains bubbles from occurring in the lubricant.

[0075] As shown in FIG. 5(b), reservoir 26 is a V-shaped recess, and end39 of shaft-tapering 31 corresponds to a bottom of the V-shaped recess.In other words, shaft-tapering 31 and reservoir 26 are positioned suchthat end 39 corresponds to the bottom of reservoir 26, whereby widerpath 34 is not shut up but runs from the vicinity of end section 33 oftapering section 6 to reservoir 26 keeping approx. the same width. Thisstructure allows the user to supply or fill the lubricant smooth intothe bearing spaces. Lubricant attached around shaft-tapering 31 iscollected to end 39 by centrifugal force and moves to radial bearingspace 24. If it splashes out, reservoir 26 accommodates it.Shaft-tapering 31 is not necessarily formed of the conical face andcylindrical face. Reservoir 26 does not necessarily shape in theV-shaped recess. However, it is essential that a part of shaft-tapering31 is opposite to a part of reservoir 26 via radial bearing space 24.

[0076] Another reservoir 26 is prepared around a center of sleeve 5,therefore, even if air enters into the bearing spaces, a given amount oflubricant can be retained in a space above a center of flange 11 and thespaces of the bearings.

[0077] Further, step 35 is provided at tapering section 6 in a thicknessdirection. Step 35 separates tapering section 6 into first tapering face36 and second tapering face 37. Recess 38 is provided at a part oftapering section 6. Recess 38 can be treated as a tapering face such asfirst and second tapering faces 36, 37.

[0078] Step 35 defines a border between two areas, one is applied withthe oil repellent and the other is not applied with it. Step 35 alsoblocks the oil repellent from entering into radial bearing space 24 viaend section 33, and works as a fence which blocks the lubricant fromsplashing out from sleeve 5. Recess 38 saves an amount of lubricant 7supposed to overflow tapering-section 6 to outside of sleeve 5.

[0079] In this fifth embodiment, tapering section 6 is constructed ofstep 35, first tapering face 36, second tapering section 37 and recess38. However, each individual element is not necessarily tapered, but theoverall structure can be tapered instead. For instance, if firsttapering face 36, provided at inner side of sleeve 5, is changed to asubstantially flat face, face 36 together with step 35 works well as areservoir for supplying or filling the lubricant into radial bearingspace 24 and thrust bearing space 40. A shape, a number and a depth ofrecess 38 can be determined considering an overall size of spindle motor1 or a size of tapering section 6.

[0080]FIG. 6 illustrates advantages of tapering section 6A, which issimilar to the tapering section 6 shown in FIG. 1 and FIG. 5(a). For theconvenience of simple description, step 35, first and second taperingfaces 36, 37, and recess 38 are omitted in FIG. 6. The overall taperingsection constructed of these elements is denoted by reference mark 6A.Shaft 8 and rotor hub 50 are the same as those shown in FIG. 1 and FIG.5(a); however, they are denoted by reference marks 8A, 50A forcorresponding to tapering section 6A.

[0081] In FIG. 6, rotor hub 50A is fixed to an end of shaft 8A at aright angle. An upper end of sleeve 5A, rotor hub 50A and shaft 8Acreate space 61, which is defined by the shapes and sizes of these threeelements.

[0082] Space 61 communicates with one space and one void, the one spaceis radial bearing space 24 and the one void is outer void 65 disposedouter side of sleeve 5. Outer void 65 works as an outlet/inlet of airfrom/to space 61, and the air is taken into space 61 via outer void 65and discharged from space 61 to outside of sleeve 5.

[0083] A shape and a size of space 61 formed by shaft 8A and rotor hub50A, both of which are positioned vertically to each other, are definedby tapering section 6A. The upper end of sleeve 5A flares from the innerside to the outer side, and the distance between tapering section 6A androtor hub 50A opposite to each other tapers from the inner side to theouter side, i.e., distance L1 is larger than distance L2. Thesedistances are determined responsive to the size of spindle motor 1. Forinstance, L1 is set at 0.3 mm and L2 is set at 0.1 mm. Thickness ofsleeve 5, i.e., distance L3 from the inner wall to the outer wall ofsleeve 5, is set at, for instance, 1.7 mm.

[0084] When shaft 8A and rotor hub 50A rotate, the centrifugal forceproduces air-flow in space 61. The air travels toward outer side ofsleeve 5A because the outer-rim speed is faster. However, the presenceof tapering section 6A changes the air-flow. To be more specific,outgoing air-flow 62 flowing from the inner side to the outer side ofsleeve 5 and incoming air-flow 63 flowing from the outer side to theinner side of sleeve 5 are produced. These air-flows produce circularair-flow 64 in space 61.

[0085] Production and power of circular air-flow 64 in space 61 dependon wind power generated by the motor rotation, distances L1, L2 at theupper end of sleeve 5, and inclination angle θ of tapering section 6A.For instance, if distance L2 is increased, air incomes/outgoes smoothto/from space 61; however, this increment of L2 influences seriously theproduction of circular air-flow 64. In particular, when outgoing volumeof air becomes greater, the production of circular air-flow 64 isprevented. Although an r.p.m. of the motor and a diameter of space 64influence somewhat, distance L2 is 1 mm at most, and preferably not morethan 0.2 mm. In the present invention, distances L1, L2 and inclinationangle θ are set at predetermined values in order to produce circularair-flow 64.

[0086] Direction of incoming air-flow 63 works as a preventer againstthe lubricant, which is oozed out of radial bearing space 24, fromsplashing out from sleeve 5A. This preventive force is influenced byinclination angle θ, and if the angle becomes smaller, the force pushingthe oozed lubricant back to the inner side of sleeve 5 is weakened. Ifthe angle becomes larger, an active area of radial bearing space 24becomes inconveniently smaller. Therefore, if a user needs a radialbearing having a predetermined capability, the user has to admit thatthe spindle motor becomes slightly larger.

[0087] Numbers of experiments were carried out in several conditionsdiscussed above, and the following appropriate condition was found.Inner diameter of the rotor hub is 30 mm, an r.p.m. of the spindle motoris around 40,000. In this condition, tapering section 6A works well as apreventer and results in an excellent sealing effect at inclinationangle θ around 5 degrees. In other words, tapering section 6A withinclination angle θ around 5 degrees practically blocks the lubricantfrom splashing out or leaking out. Further, application of oil repellentto tapering section 6A lowers the surface tension, so that the blockingeffect increases remarkably. To be more specific, if the force ofincoming air-flow 63 is not more than 2 μN, tapering section 6A can pushsubstantially the lubricant back to the inner side of sleeve 5.

[0088] The description hereinbefore proves that the present inventioncan provide a thrust bearing which can substantially bear an axial loadof a shaft because a flange, having a larger diameter than that of theshaft, is prepared. The thrust bearing is located between the flange anda thrust plate opposite closely to the flange. A tapering section isprovided on an upper end of the sleeve, and the tapering section blockslubricant from splashing out or leaking out from the sleeve.

[0089] A distance between the tapering section and a rotor hub isnarrowed along a radial direction from an inner side to an outer side ofthe sleeve. This structure produces incoming air-flow running to theinner side along a face of the rotor hub opposite to the sleeve, so thatthe lubricant is blocked from oozing out inconveniently on the face ofthe rotor hub. Another taper is provided to the shaft at a place suchthat the tapering section on the sleeve is actually widened. Therefore,an enough space is prepared for applying the lubricant, and a pressureapplied to the lubricant is lowered, which prevents bubbles fromoccurring and supplies the lubricant to the reservoir in a substantialamount.

[0090] Since the flange has a larger diameter than that of the shaft,the thrust bearing, which can substantially bear the axial load of theshaft, is constructed. The thrust bearing is located between the flangeand the thrust plate opposite closely to the flange. The taperingsection on the upper end of the sleeve reserves a space large enough forstoring lubricant to be filled into the bearing space, and blocks thelubricant from leaking out from the sleeve.

[0091] A nearly closed space is formed between the rotor hub and theupper end of the sleeve. Incoming air-flow to the inner side of thesleeve is thus generated, which blocks the lubricant from leaking, orsplashing out from the inner side to the outer side of the sleeve.

[0092] Circular air-flow can be produced in the space discussed above,and the circular air-flow flows against the splashing direction (insideto outside) of the lubricant. The circular air-flow thus restraints thelubricant from leaking out or splashing out from the inner side to theouter side of the sleeve.

[0093] The lubricant travels along the tapering section upward forleaking or splashing out from the sleeve; however, air-flow against thismovement is produced on the upper end of the sleeve. This air-flowpushes the lubricant back to the inner side, and blocks the lubricantfrom splashing out.

[0094] Oil repellent lowers surface tension, thus application of the oilrepellent to the tapering section can restraint the lubricant fromleaking or splashing out from the sleeve even if the air-flow forcetoward the inner side is not enough. Because the oil repellent repelsthe lubricant, even if surplus lubricant spreads out, it can be wipedoff with ease.

[0095] A step provided to the tapering section defines a border betweentwo areas, one is applied by the oil repellent and the other is notapplied. The step also works as a fence which blocks the oil repellentfrom entering into the radial bearing space and the thrust bearingspace.

[0096] The step also assists the lubricant to flow smooth into thereservoir from the tapering section. Shaft-tapering supplements thefunction of the tapering section provided on the upper end of thesleeve. To be more specific, the tapering section on the upper end ofthe sleeve works as a reservoir which supplies or fills the lubricantinto the radial bearing space and the thrust bearing space. If aninclination angle of the tapering section is small, the tapering sectiondoes not work well as the reservoir. In such a case, the shaft-taperingsupplements the function of reservoir. When a taper is prepared on apart of the shaft, the space for retaining the lubricant is enlarged.Thus a pressure applied to the lubricant decreases, which restrainsbubbles from occurring.

[0097] The shaft-tapering communicates with the reservoir provided atthe inner side of the sleeve with approx. the same width of distance,therefore, the space for retaining the lubricant is enlarged. As aresult, the lubricant can be supplied smooth to the bearing spaces, andthe pressure applied to the lubricant decreases, thereby restrainingbubbles from occurring.

[0098] The space extending from the upper end of the sleeve to thereservoir is not shut up, but keeps wide, therefore, the lubricant canbe supplied or filled smooth into the radial bearing space and thethrust bearing space.

[0099] The advantages of the present invention discussed above are, inshort, to save surplus supplement of lubricant, to prevent gas fromoccurring in the lubricant. As a result, a spindle motor of a longerservice life is obtainable, which contributes a lot to the industry.

What is claimed is:
 1. A spindle motor comprising: (a) a shaft; (b) aflange fixed to a first axial end of said shaft and having a largerdiameter than said shaft; (c) a cylindrical sleeve to which said shaftis fit, said sleeve having a tapering section on an upper end thereof;(d) a radial bearing space formed between faces of said shaft and saidsleeve, the faces opposite closely to each other; (e) a rotor hub fixedto a second axial end of said shaft and disposed opposite to an upperend of said sleeve; (f) a thrust plate disposed opposite closely to saidflange; (g) a thrust bearing space formed between faces of said flangeand said thrust plate, the faces opposite closely to each other; and (h)lubricant retained in said thrust bearing space.
 2. The spindle motor ofclaim 1, wherein a distance between said rotor hub and the taperingsection on the upper end of said sleeve narrows along an axial directionfrom an inner side toward outer side of said sleeve.
 3. The spindlemotor of claim 1 or claim 2 further comprising a space surrounded bysaid shaft, said rotor hub and the upper end of said sleeve, whereinsaid space becomes smaller along the axial direction from the inner sidetoward the outer side of said sleeve.
 4. The spindle motor of claim 3,wherein air-flow is generated in said space, and the air-flow has twodirections, one flows from the inner side toward the outer side of saidsleeve and another flows from the outer side toward inner side of saidsleeve.
 5. The spindle motor of claim 4, wherein the air-flow flowingfrom the outer side toward the inner side of said sleeve flows downalong a slope of the tapering section of said sleeve.
 6. The spindlemotor of any one of claims 1 through 5, wherein oil repellent is appliedto the tapering section on the upper end of said sleeve.
 7. The spindlemotor of claim 1 or claim 2, wherein a step is provided to a part of thetapering section on the upper end of said sleeve.
 8. The spindle motorof claim 1 or claim 2, wherein a wider path is prepared near to an endof the tapering section on the upper end of said sleeve, and the widerpath works as a lubricant reservoir.
 9. The spindle motor of claim 1 orclaim 2,wherein a taper is provided on an outer wall of said shaft at aplace close to an end of the tapering section.
 10. The spindle motor ofclaim 1 or claim 2, wherein a wider path is prepared near to an end ofthe tapering section on the upper end of said sleeve, and the wider pathworks as a lubricant reservoir,wherein a taper is provided on an outerwall of said shaft at a place close to an end of the tapering section,wherein the reservoir is disposed on an inner wall of said sleeve at aplace corresponding to the taper provided to said shaft via said radialbearing space.
 11. The spindle motor of claim 10, wherein the taperprovided to said shaft is opposite to a part of the reservoir preparedon the inner wall of said sleeve via said radial bearing space.